﻿<p>An <em>IfcSweptDiskSolid</em> represents the 3D shape by a sweeping representation scheme allowing a two dimensional
circularly bounded plane to sweep along a three dimensional <em>Directrix</em> through space.</p>
<p>The <em>StartParam</em> and <em>EndParam</em> parameter are optional, if not provided they default to the start and
end of the <em>Directrix</em>. Only if the <em>Directrix</em> is given by a bounded or by a closed curve, it is
permissible to omit the values of <em>StartParam</em> and <em>EndParam</em>.</p>
<p>If the transitions between consecutive segments of the <em>Directrix</em> are not tangent continuous, the resulting
solid is created by a miter at half angle between the two segments. Informal proposition restricts the permissible
angle between two non-tangent continuous segments.</p>
<p>Figure 2 illustrates an example.</p>
<ul>
<li><em>Directrix</em> given as <em>IfcIndexedPolyCurve</em>, having linear and circular arc segments, that are tangent continuous between each segments</li>
<li><em>Directrix</em> being a bounded and open curve</li>
<li>No <em>StartParam</em> and <em>EndParam</em> are provided, start and end default to start and end of the bounded
curve of the <em>Directrix</em></li>
</ul>
<blockquote class="note">NOTE&nbsp; Although the example shows a <em>Directrix</em> as a poly curve on a planar
reference surface, the definition of <em>IfcSweptDiskSolid</em> is not restricted to be based on planer curves. However
view definitions or implementer agreements may provide restrictions.</blockquote>
<blockquote class="note">NOTE&nbsp; The geometric item <em>IfcIndexedPolyCurve</em> provides a more compact representation compared with <em>IfcCompositeCurve</em> as is therefore the prefered curve representation for the <em>Directrix</em>.</blockquote>
<table border="0" cellpadding="2" cellspacing="2" summary="disk solid usage">
<tr>
<td><img src="../../../figures/ifcsweptdisksolid-layout1.png" alt="disk solid"></td>
</tr>
<tr>
<td>
<p class="figure">Figure 2 &mdash; Swept disk solid geometry</p>
</td>
</tr>
</table>
<blockquote class="extDef">NOTE&nbsp; Definition according to ISO/CD 10303-42:1992<br>
A swept disk solid is the solid produced by sweeping a circular disk along a three dimensional curve. During the
sweeping operation the normal to the plane of the circular disk is in the direction of the tangent to the directrix
curve and the center of the disk lies on the directrix. The circular disk may, optionally, have a central hole, in this
case the resulting solid has a through hole, or, an internal void when the directrix forms a close curve.</blockquote>
<blockquote class="note">NOTE&nbsp; Entity adapted from <strong>swept_disk_solid</strong> defined in ISO
10303-42.</blockquote>
<blockquote class="history">HISTORY&nbsp; New entity in IFC2x2.</blockquote>
<blockquote class="change-ifc2x4">IFC4 CHANGE&nbsp; The attribute <em>StartParam</em> and <em>EndParam</em> have been
made optional.</blockquote>
<p class="spec-head">Informal Propositions:</p>
<ol>
<li>If the <em>Directrix</em> curve definition is not tangent continuous, the transition between the segments has to be
within an acceptable limit of tangent discontinuity. Very sharp edges may result in nearly impossible miter.
Implementer agreements may define acceptable limits for tangent discontinuity.</li>
<li>The segments of the <em>Directrix</em> shall be long enough to apply the <em>Radius</em>. In case of an arc segment
forming part of the <em>Directrix</em>, its radius shall be greater then the disk <em>Radius</em></li>
<li>The <em>Directrix</em> shall not be based on an intersecting curve.</li>
</ol>